The present disclosure relates generally to the field of power supplies for information handling systems, and more particularly to techniques for efficiently providing power to drive a discharge lamp, such as a cold cathode fluorescent lamp (CCFL).
As the value and use of information continues to increase, individuals and businesses seek additional ways to acquire, process and store information. One option available to users is information handling systems. An information handling system (IHS) generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Liquid crystal display (LCD) panel based display devices have been commonly utilized in many IHS systems due to their compact size, and low power consumption. Although there are different types of backlights (e.g., light sources including a discharge lamp), which are currently used for backlighting the latest LCD panels, the CCFL (also known as cold cathode fluorescent tube (CCFT)) is most commonly used. Circuits for supplying power to CCFL's generally require a controllable alternating current (AC) power supply and a feedback loop to accurately monitor the current in the lamp in order to maintain operating stability of the circuit and to have an ability to vary the lamp brightness. Such circuits typically generate a high voltage to initially turn on the CCFL and then lower the voltage when current begins to flow through the lamp.
Such circuits also typically include an inverter circuit to convert a direct current (DC) voltage received as an input to a regulated AC current generated as an output. Inverter circuits typically include a controller component, such as a pulse width modulator (PWM) based controller. Various well-known inverter circuit configurations or “topologies” include a Royeroscillator, full-bridge or half-bridge inverters.
The CCFL power consumption may account for a significant portion (e.g., up to 50% in some cases) of the IHS system power requirement, especially for portable systems. Therefore, there is a considerable amount of interest to achieve advantages in extending battery life and reducing re-charge frequency by improving the efficiency of power supplies configured to provide power to the CCFL.
Traditional inverter circuits may use a single stage or two stage inverter. FIG. 1 illustrates a block diagram for a commercially available two stage inverter 100, such as model 1NVC638 LCD backlight inverter manufactured by Hitachi Media Electronics. In such inverters, the output of a first stage DC—DC booster, which is provided as an input to a second stage inverter, is held substantially constant. The second stage includes a resonant push-pull inverter. The traditional two stage inverter regulates the output (current provided to the CCFL load) by varying the duty cycle to the first stage. The second stage operates at a fixed frequency and duty cycle, independently of the first stage duty cycle.
Presently, many single stage and two stage inverters do not maintain high efficiency over wide variations in input voltage. In traditional inverter based power circuits, a wider input voltage range, and/or a larger difference between the input and output voltages typically causes a decrease in power conversion efficiency.
Historically, the battery cell stacks and cell technology have determined the range of input voltage provided to the first stage. Presently, a voltage range for battery cell stacks working in combination with AC/DC adaptors typically varies from 9V–22V. With the trend towards lowering battery cell stack voltages, in the near term, maturing battery technology may extend this range to 6V–22V. Further advances in battery technology may cause the low end of the voltage range to drop even further. This typically results in generating more heat in the inverter thereby reducing battery run time.
Therefore, a need exists for improved efficiency of the power circuits providing power to the CCFL. More specifically, a need exists to develop tools and techniques for improving the efficiency of inverters under changing input voltage. Accordingly, it would be desirable to provide tools and techniques for an improved inverter of an IHS absent the disadvantages found in the prior methods discussed above.